A foundation for success

With revered researchers such as Laureate Professor Scott Sloan and Professor John Carter leading the way, geotechnical engineering at the University of Newcastle is on solid ground.

Most drivers on the Pacific Highway would give little thought to the towering embankments that line the newly upgraded sections of the road along the NSW North Coast, but to engineers they represent a significant accomplishment.

As University of Newcastle Laureate Professor Scott Sloan explains, some of the embankments stand on soil that is very unstable and pose major engineering problems.

"Stepping onto coastal soft soils, you can sometimes sink to your knees," says Sloan, a geotechnical engineer and internationally recognised expert in soil stability analysis. "It is a massive engineering challenge to build major infrastructure on this type of foundation, in reasonable time and
at reasonable cost."

The problem is typical of the troubleshooting nature of geotechnical engineering, which focuses on predicting the behaviour of earth materials to ensure stability for buildings and infrastructure.

Under Sloan's leadership, the University has long been a leader in computational modelling in the field. His development of faster and more efficient methods of calculating the load capacity for buildings and structures has drawn acclaim from around the world. User-friendly software developed by Sloan
is set for international commercial release next year through Newcastle Innovation, the University's commercial arm.

Sloan is the director of the University's Centre for Geotechnical and Materials Modelling and also leads the new Australian Research Council (ARC) Centre of Excellence in Geotechnical Science and Engineering. With funding of $14.4 million over seven years, the collaborative Centre for Excellence will
specialise in developing new and improved tools for designing energy and transport infrastructure in a cost-effective manner.

The Centre combines the theoretical and computational strengths of the Newcastle research centre; the University of Wollongong's knowledge in below-track rail infrastructure; and the offshore expertise and experimental capabilities of the University of Western Australia, which has Australia's only
geotechnical centrifuge modelling facility.

The collaboration represents a professional reunion of sorts for Sloan and his colleagues Professor John Carter, Newcastle's Pro Vice-Chancellor of Engineering and Built Environment, and Professor Mark Randolph, the former head of the University of Western Australia's Centre for Offshore Foundation
Systems. All were researchers at Cambridge 30 years ago and each has gone on to build a distinguished academic and research career. The three are among the select few engineers who have been made Fellows of the Australian Academy of Science.

One of the initial joint projects under the ARC Centre for Excellence program will be the establishment of Australia's first national soft soil test site, near Ballina, on the NSW North Coast. Working with the Roads and Traffic Authority and industry partners, researchers will explore stability problems
that have been experienced during the $5.0 billion Pacific Highway upgrade.

"This represents a significant challenge for engineers today because much of the east coast of Australia has problematic soft soils. Stable land along the coast is becoming increasingly scarce, forcing major transport and energy infrastructure projects onto marginal land where the soil can be very
soft," Sloan says.

The ARC Centre for Excellence will also direct its research to safety analysis of offshore oil and gas developments on soft sea floors, an area in which Carter and colleagues from the University of Western Australia have significant expertise. For example, Carter has worked across the globe, from the
oil platforms in the North Sea and to those on Australia's North West Shelf, and has consulted for BHP, Esso, Woodside Wapet, Bond Oil, Amoco and Exxon.

Some of his most challenging work was on the North Rankin A and Goodwyn platforms off Western Australia in the 1980s. Those early offshore projects in Australia were problematic, Carter explains, largely because the properties of the soft carbonate soils on the seabed were not well understood. Remediation
work on the platforms ended up costing more than $500 million. However, as with most first-time projects, it proved to be a great learning ground for researchers and project engineers.

"It is often the case in engineering that you learn most when something goes wrong," Carter says.

Carter and Sloan are accomplished computational engineers whose mathematical models have been widely adopted into engineering practice. Both have received broad recognition from within their profession and beyond. Carter, named last year one of Australia's 100 most influential engineers,
was particularly proud and humbled when he received an Order of Australia in 2006. Sloan nominates being invited to give this year's Rankine Lecture in England, one of the most prestigious honours in geotechnics, as a career highlight.

Both Sloan and Carter are enthusiastic advocates of the cross-disciplinary nature of research groups such as the research centre and Centre for Excellence.

"On any research project you will have a lot of people who work on the fringes," Carter says. "These centres encourage researchers from different disciplines to come together and allow for the better exchange of ideas and expertise between departments and institutions."

Sloan says the ARC Centre for Excellence adds to the already solid reputation of the University of Newcastle in geotechnical engineering.

"The geotechnical research group at this University is arguably the strongest in the country and one of the strongest internationally," he says.

"People want to come here to do their research. It has become a destination for the brightest and best in the world."

Career Summary

Biography

Scott Sloan works in the broad area of computational geomechanics, with a particular interest in geotechnical stability analysis. He is currently the Director of an ARC Centre of Excellence on Geotechnical Science and Engineering and an ARC Laureate Fellow. He also holds the title of Laureate Professor at the University of Newcastle, one of three in the Faculty of Engineering and Built Environment.

Research ExpertiseBroad area of geotechnical engineering, with a special emphasis on computational methods. Expertise in nonlinear finite element analysis, computational limit and shakedown analysis, linear and nonlinear optimisation methods, constitutive modelling of geomaterials, unsaturated soils, plasticity theory, and contaminant migration in soils.

Invitations

Participant

13th International Conference of the International Association for Computer Methods and Advances in Geomechanics, Melbourne Organisation: International Association for Computer Methods and Advances in Geomechanics
Description:
Invited by IACMAG

2010

9th World Congress on Computational MechanicsOrganisation: International Association for Computational Mechanics
Description:
The world's largest conference on computational mechanics

2008

12th International Conference of the International Association for Computer Methods and Advances in Geomechanics, GoaOrganisation: International Association for Computer Methods and Advances in Geomechanics
Description:
Invited by IACMAG

2008

8th World Congress on Computational Mechanics, VeniceOrganisation: International Association for Computational Mechanics
Description:
Invited by IACM

2005

Finite element limit analysis in geomechanicsOrganisation: 11th International Conference of the International Association for Computer Methods and Advances in Geomechanics (IACMAG 2005), Torino
Description:
Invited by IACMAG Board

2004

Geotechnical stability analysis: new methods for an old problemOrganisation: Australian Geomechanics Society
Description:
Invited by Australian Geomechanics Society

Industrial wastewaters often consist of a complex chemical cocktail with treatment of target contaminants complicated by adverse chemical reactions. The impact of metal ions (Cd<s... [more]

Industrial wastewaters often consist of a complex chemical cocktail with treatment of target contaminants complicated by adverse chemical reactions. The impact of metal ions (Cd2 +, Ba2 + and Mn2 +) on the kinetics of fluoride removal from solution by natural zeolite was investigated. In order to better understand the kinetics, the pseudo-second order (PSO), Hill (Hill 4 and Hill 5) and intra-particle diffusion (IPD) models were applied. Model fitting was compared using the Akaike Information Criterion (AIC) and the Schwarz Bayesian Information Criterion (BIC). The Hill models (Hill 4 and Hill 5) were found to be superior in describing the fluoride removal processes due to the sigmoidal nature of the kinetics. Results indicate that the presence of Mn (100 mg L- 1) and Cd (100 mg L- 1) respectively increases the rate of fluoride sorption by a factor of ~ 28.3 and ~ 10.9, the maximum sorption capacity is increased by ~ 2.2 and ~ 1.7. The presence of Ba (100 mg L- 1) initially inhibited fluoride removal and very poor fits were obtained for all models. Fitting was best described with a biphasic sigmoidal model with the degree of inhibition decreasing with increasing temperature suggesting that at least two processes are involved with fluoride sorption onto natural zeolite in the presence of Ba. Crown

The consolidation behavior of ground with vertical drains is known to be greatly affected by the finite permeability of the sand drains, also called the effect of well resistance.... [more]

The consolidation behavior of ground with vertical drains is known to be greatly affected by the finite permeability of the sand drains, also called the effect of well resistance. However, up to now, no analytical methods have been reported for evaluating this effect on the nonlinear consolidation behavior of vertical drains. In this paper, by considering the nonlinear compressibility and permeability of soil during consolidation, the effect of well resistance was incorporated into the derivation of the equations that govern the nonlinear consolidation of a vertical drain with coupled radial-vertical flow. In addition, the smear effect was considered by assuming three decay patterns for the radial permeability coefficients of the soil toward the sand drain in the smeared zone. After obtaining the governing equations, a simplified analytical solution is derived for a general time-variable surcharge loading. Based on the general solution obtained, detailed solutions are provided for three special types of loading schemes: constant loading, single-stage loading, and multi-stage loading. The validity of the solution is verified by reducing it to several special cases and comparing these to existing solutions. Finally, the effect of the well resistance, the ratios of the compression index to the radial and vertical permeability indices, various loading schemes, and various variation patterns of the radial permeability coefficient of the soil in the smeared soil zone are investigated using parametric analysis.

A comprehensive numerical study on finite element implementation of hypoplastic models is presented. Two crucial aspects, local integration of the constitutive equations (the loca... [more]

A comprehensive numerical study on finite element implementation of hypoplastic models is presented. Two crucial aspects, local integration of the constitutive equations (the local problem) and forming tangent operators for Newton-Raphson iteration (the global problem), are investigated. For solving the local problem, different integration algorithms, including explicit and implicit methods, are examined using tri-axial compression tests and incremental stress response envelopes, as well as typical boundary value problems. For solving global problems, three different ways of generating the tangent operator are compared. The numerical evidences indicate that, in terms of accuracy, efficiency and robustness, explicit methods with substepping and error control are the best choices for constitutive integration of hypoplastic models while the so-called continuum tangent operators have certain advantages over two other types of numerically-generated consistent tangent operators.

Solowski WT, Sloan SW, 'Evaluation of material point method for use in geotechnics', International Journal for Numerical and Analytical Methods in Geomechanics, 39 685-701 (2015)

The first part of the paper presents a material point method solution for the bearing capacity of a deep foundation in purely cohesive soil, which is a widely known engineering pr... [more]

The first part of the paper presents a material point method solution for the bearing capacity of a deep foundation in purely cohesive soil, which is a widely known engineering problem. The results computed with the generalised interpolation material point method are compared to the results obtained previously with an advanced limit analysis code. The second part of the paper shows material point method simulations of collapsing piles of granular material and compares the results with experimental observations from the literature. The problems considered are problematic to solve using the displacement finite element method as they generally include very large deformations.

Experimental studies and numerical modelling of the deformation of soft clay stabilised by stone columns have been conducted over the past few decades. Continuum-based numerical m... [more]

Experimental studies and numerical modelling of the deformation of soft clay stabilised by stone columns have been conducted over the past few decades. Continuum-based numerical models have provided valuable insight into the prediction of settlement, lateral deformation, and stress and strain-rate dependent behaviour of stone columns at a macroscopic scale, but because they consist of granular material such as crushed rock, gravel, and waste rock aggregates, their behaviour is influenced by inter-particle micromechanics and cannot be modelled properly using these models. In this paper a novel coupled model of the discrete element method (DEM) and finite difference method (FDM) is presented to study the deformation of a single stone column installed in soft ground. In this coupled discrete-continuum method, PFC2D and FLAC were used to model the interaction between the stone column and surrounding clay, respectively. The contact forces at the interface between the two zones were determined through a socket connection that allows the DEM to transfer forces and moments to the FDM and vice versa. The predicted results were comparable to the data measured experimentally, showing that the coupled discrete-continuum model proposed in this study could simulate the load-deformation behaviour of a stone column installed in clay. The contact force distribution and shear stress contour developed in the stone column and surrounding clay were captured to provide a better understanding of the load-deformation behaviour of the stone column.

The mechanical properties of dry soil mix (DSM) columns can be highly variable. Variability can be accounted for in the construction specification for deterministic design and dir... [more]

The mechanical properties of dry soil mix (DSM) columns can be highly variable. Variability can be accounted for in the construction specification for deterministic design and directly in reliability based design. Design methods and specifications to date adopt simplifications that do not take the variability of the columns fully into account. This paper uses both simple and advanced probabilistic methods to assess the performance/failure and system redundancy of dry soil mix columns. Reliability-based design methods and examples are given for the design of column strength and the adjustment of the column spacing to achieve a target probability of unacceptable performance or failure. An acceptance criteria chart is developed. The pull-out resistance tests on the DSM columns constructed for the Ballina Bypass motorway construction project in NSW Australia are compared to the chart to provide guidance with respect to acceptance criteria required to achieve the desired performance.

By incorporating the nonlinear variation of a soil's compressibility and permeability during the process of consolidation, an analytical solution for the radial consolidation of v... [more]

By incorporating the nonlinear variation of a soil's compressibility and permeability during the process of consolidation, an analytical solution for the radial consolidation of vertical drains has been developed for a general time-variable loading. The general solution was verified for the cases of instantaneous loading and ramp loading. Detailed solutions were further derived for two special loading schemes: multistage loading and preloading-unloading-reloading. The nonlinear consolidation behavior of a vertical drain subjected to these two types of loading schemes was then investigated by a parametric study. The results show that the loading rate, the ratio of the compressibility index to the permeability index (Cc/Ck), and the initial stress state have a significant influence on the consolidation rate. A smaller value of Cc/Ck, a larger initial stress, or a fast loading rate always leads to a rapid consolidation rate. During the unloading period, a negative excess pore water pressure may occur, and a slower unloading rate may reduce this negative value.

In this paper, finite element limit analysis (FELA) and semi-analytical rigid block techniques are used to investigate the influence of tunnel spacing on the undrained stability o... [more]

In this paper, finite element limit analysis (FELA) and semi-analytical rigid block techniques are used to investigate the influence of tunnel spacing on the undrained stability of two unlined square tunnels constructed side by side. The tunnels, which are assumed to be straight and infinitely long, are modelled under conditions of plane strain. Upper and lower bounds on the stability of the tunnels are obtained using FELA; the numerical formulation of which is based upon the bounds theorems of classical plasticity. These bounds, which bracket the true collapse load from above and below, are found to be in good agreement with one another. Rigid block methods also provided an upper bound estimate on tunnel stability which was generally higher than, but still in good agreement with, the FELA upper bound. Failure mechanisms associated with the collapse of the dual tunnels were investigated, and for deeper tunnels, it was found that mechanisms extend much deeper below the tunnels than the collapse mechanisms associated with a single tunnel. Results from this study are summarised in dimensionless stability charts for use by practitioners.

We investigate numerically the mechanisms governing horizontal dragging of a rigid cylinder buried inside granular matter, with particular emphasis on enumerating drag and lift forces that resist cylinder movement. The recently proposed particle finite element method is employed, which combines the robustness of classical continuum mechanics formulations in terms of representing complex aspects of the material constitutive behavior, with the effectiveness of discrete element methods in simulating ultralarge deformation problems. The investigation focuses on the effect of embedment depth, cylinder roughness, granular matter macromechanical properties, and of the magnitude of the cylinder's horizontal displacement on the amplitude of the resisting forces, which are discussed in light of published experimental data. Interpretation of the results provides insight on how the material flow around the cylinder affects the developing resistance, and a mechanism is proposed to describe the development of a steady-state drag force at large horizontal movements of the cylinder.

Experimental data on Lower Cromer Till (LCT), a sandy silty-clay, are re-evaluated enabling a study on the effects of plastic anisotropy of soil fabric. The results of virgin cons... [more]

Experimental data on Lower Cromer Till (LCT), a sandy silty-clay, are re-evaluated enabling a study on the effects of plastic anisotropy of soil fabric. The results of virgin constant stress ratio consolidation tests reveal that an equilibrium state is achieved and maintained under any specific radial loading path, with characteristics of a unique anisotropic fabric and a unique straining mode. The inclination of the plastic dilatancy and the yield surface from the hydrostatic axis provides a means of quantifying this equilibrium state of the soil fabric. A unique fabric anisotropy at critical state is naturally obtained. Rotational hardening laws are then proposed to quantify the changes in plastic anisotropy of soil fabric for all stress ranges. Constitutive relations are formulated within the framework of Critical Sate Soil Mechanics, with a non-associated flow rule logically determined from experiments. The proposed rotational hardening laws have been systematically validated against a large bank of laboratory tests on LCT samples, covering a variety of deposition conditions, stress histories, and overconsolidation ratios. Comparisons illustrate the feasibility and efficiency of the proposed framework in describing the plastic anisotropy of LCT, which may suggest possible application to other types of clays.

In practical geotechnical engineering the factor of safety is still determined by means of simple limit equilibrium analysis in many cases. However, because displacement finite-el... [more]

In practical geotechnical engineering the factor of safety is still determined by means of simple limit equilibrium analysis in many cases. However, because displacement finite-element analysis is routinely applied for assessing displacements and stresses for working load conditions, this technique is increasingly being used to calculate ultimate limit states and, consequently, factors of safety, usually by means of the so-called strength reduction technique, and results which are comparable to those obtained with limit equilibrium methods have been reported in the literature. However, owing to the inherent assumptions of limit equilibrium analyses, they do not always provide unique factors of safety. The purpose of this paper is on the one hand to compare the strength reduction method with rigorous limit analyses which are based on collapse theorems of plasticity, and on the other hand to investigate if a shortcoming of the strength reduction method, namely possible numerical instabilities for non-associated plasticity, can be overcome. Two examples are considered, namely slope stability and tunnel face stability. Finally an important note on the definition of the factor of safety for effective and total stress analysis under undrained conditions is provided.

Summary: A finite element algorithm for frictionless contact problems in a two-phase saturated porous medium, considering finite deformation and inertia effects, has been formulated and implemented in a finite element programme. The mechanical behaviour of the saturated porous medium is predicted using mixture theory, which models the dynamic advection of fluids through a fully saturated porous solid matrix. The resulting mixed formulation predicts all field variables including the solid displacement, pore fluid pressure and Darcy velocity of the pore fluid. The contact constraints arising from the requirement for continuity of the contact traction, as well as the fluid flow across the contact interface, are enforced using a penalty approach that is regularised with an augmented Lagrangian method. The contact formulation is based on a mortar segment-to-segment scheme that allows the interpolation functions of the contact elements to be of order N. The main thrust of this paper is therefore how to deal with contact interfaces in problems that involve both dynamics and consolidation and possibly large deformations of porous media. The numerical algorithm is first verified using several illustrative examples. This algorithm is then employed to solve a pipe-seabed interaction problem, involving large deformations and dynamic effects, and the results of the analysis are also compared with those obtained using a node-to-segment contact algorithm. The results of this study indicate that the proposed method is able to solve the highly nonlinear problem of dynamic soil-structure interaction when coupled with pore water pressures and Darcy velocity.

This paper presents a numerical study of shear localization in granular materials based on a discrete element method. The plane Couette shear test is proposed for this purpose. A ... [more]

This paper presents a numerical study of shear localization in granular materials based on a discrete element method. The plane Couette shear test is proposed for this purpose. A numerical model is established to simulate the test. With the flexible side boundaries, it is demonstrated that the plane Couette shear state can be achieved within a granular sample of limited length, and a shear band parallel to the shear direction can be obtained. Numerical results are also presented to show the formation and the development of the shear band. A homogenization procedure is employed for presenting the variation of the field variables such as stress components, the couple stress, the void ratio and the grain rotation. The evolution and the spatial distribution of these quantities are qualitatively in accordance with the Cosserat continuum model predictions. The numerical results also indicate that the Cosserat effect plays a vital role in shear localization zone.

Slope stability analyses in practical geotechnical engineering are predominantly performed using limit equilibrium methods, despite the inherent shortcoming that the form of the f... [more]

Slope stability analyses in practical geotechnical engineering are predominantly performed using limit equilibrium methods, despite the inherent shortcoming that the form of the failure mechanism has to be defined a priori. This assumption is not needed when more advanced methods, such as limit analyses or displacement-based finite element methods, are employed for calculating factors of safety and thus the advantages of these methods are increasingly recognized. However, the latter may suffer from numerical instabilities when using non-associated plasticity whereas the former are restricted to associated flow rules. This paper shows that these issues may be overcome by a modification of the so-called Davis approach which provides accurate estimates of the factor of safety of slopes, even for extreme cases of steep slopes with friction angles in excess of 40Â° and zero dilatancy.

Rock joints exert an enormous influence on the permeability of a rock mass because they act as interconnecting networks that provide pathways for fluids to permeate and flow withi... [more]

Rock joints exert an enormous influence on the permeability of a rock mass because they act as interconnecting networks that provide pathways for fluids to permeate and flow within the rock structure. The apertures in rock joints are irregular in nature and induce flows that cannot be described by the parallel-plate theory based on planar joints or the classical cubic flow relationships. In this study, a two-dimensional (2D) hydraulic aperture distribution was considered to develop a mathematical model for fracture flow. In this approach, the three-dimensional Navier-Stokes equation was integrated over the joint aperture and converted to an equivalent 2D flow model. The proposed model was then solved numerically by adopting a well-known algorithm for coupling the pressure and velocity and implementing it in a computer program. The selected program is capable of predicting the deformation of the joint apertures on normal loading, the resulting flow patterns, and the volumetric flow rates associated with permeability tests conducted using a high-pressure triaxial apparatus that was designed and built at the University of Wollongong. The model output for different conditions of confining stresses and hydraulic gradients was computed, and a good agreement with the experimental results was observed.

We present an analytical study on the vertical vibration of an elastic pile embedded in poroelastic soil. The poroelastic soil is divided into a homogeneous half-space underlying ... [more]

We present an analytical study on the vertical vibration of an elastic pile embedded in poroelastic soil. The poroelastic soil is divided into a homogeneous half-space underlying the pile base and a series of infinitesimally thin independent layers along its shaft. The dynamic interaction problem is solved by extending a method originally proposed for an embedded rigid foundation. The validity of the derived solution is verified via comparison with existing solutions. Arithmetical examples are used to demonstrate the sensitivity of the vertical pile impedance to the relative rigidity of the two soil parts.

The consolidation behavior of ground with vertical drains is known to be greatly affected by the finite permeability of the sand drains, also called the effect of well resistance.... [more]

The consolidation behavior of ground with vertical drains is known to be greatly affected by the finite permeability of the sand drains, also called the effect of well resistance. However, up to now, no analytical methods have been reported for evaluating this effect on the nonlinear consolidation behavior of vertical drains. In this paper, by considering the nonlinear compressibility and permeability of soil during consolidation, the effect of well resistance was incorporated into the derivation of the equations that govern the nonlinear consolidation of a vertical drain with coupled radial-vertical flow. In addition, the smear effect was considered by assuming three decay patterns for the radial permeability coefficients of the soil toward the sand drain in the smeared zone. After obtaining the governing equations, a simplified analytical solution is derived for a general time-variable surcharge loading. Based on the general solution obtained, detailed solutions are provided for three special types of loading schemes: constant loading, single-stage loading, and multi-stage loading. The validity of the solution is verified by reducing it to several special cases and comparing these to existing solutions. Finally, the effect of the well resistance, the ratios of the compression index to the radial and vertical permeability indices, various loading schemes, and various variation patterns of the radial permeability coefficient of the soil in the smeared soil zone are investigated using parametric analysis.

This paper presents details of the advancements of the Australian Research Council Centre of Excellence for Geotechnical Science and Engineering to the apparatus, facilities and m... [more]

This paper presents details of the advancements of the Australian Research Council Centre of Excellence for Geotechnical Science and Engineering to the apparatus, facilities and methods for physical modelling in geotechnics. This advancement includes (i) the launch of a National Geotechnical Centrifuge Facility with a new 10 m diameter fixed beam centrifuge that will be capable of spinning 2.4 tonnes of soil at 100 gravities, (ii) a new mobile soft soil in situ testing laboratory, (iii) a new national facility for the cyclic testing of high-speed rail and (iv) three recirculating flumes, called O-tubes, which are presented in another paper of this special issue. This paper provides an overview of this new equipment and the aims of the research that it will underpin. The equipment will provide enhanced possibilities for Australia to conduct project specific testing for future energy and transportation infrastructure developments, nationally and internationally.

The observational method is one of the most successful processes in geotechnical engineering. Performance monitoring data are the most reliable information that engineers can use ... [more]

The observational method is one of the most successful processes in geotechnical engineering. Performance monitoring data are the most reliable information that engineers can use to predict future performance of geotechnical projects. This paper presents two examples where Bayesian statistical methods can be used for the prediction of future performance. The first example is to update the capacity of piles using load test results. The second example is to update embankment settlement predictions when field settlement monitoring data are available.

Economic growth in Australia and the rest of the world is linked to the scale of construction and mining, and the amount of earth moved each year in these operations is difficult ... [more]

Economic growth in Australia and the rest of the world is linked to the scale of construction and mining, and the amount of earth moved each year in these operations is difficult to fathom. When distributed evenly across the world's population, each individual moves several tonnes of earth each year. This paper highlights current and future research initiatives within the ARC Centre of Excellence for Geotechnical Science and Engineering (CGSE) aimed at developing rigorous, mechanics-based models for fundamental ploughing and cutting processes in soils. State-of-the-art physical modelling is integrated with the development of new techniques for analytical and numerical modelling to elucidate and predict the full progression of forces and deformations in both two-dimensional and three-dimensional processes. A new analytical model for cutting in dry sand is presented, and preliminary results from numerical and physical modelling are described. The analyses reveal effects that available models fail to consider and illustrate how the development of rigorous models may facilitate improvements in production and efficiency in earthmoving operations.

The diametrical compression of a circular disc (Brazilian test) or cylinder with a small eccentric hole is a simple but important test to determine the tensile strength of rocks. ... [more]

The diametrical compression of a circular disc (Brazilian test) or cylinder with a small eccentric hole is a simple but important test to determine the tensile strength of rocks. This paper studies the failure mechanism of circular disc with an eccentric hole by a 3D numerical model (RFPA3D). A feature of the code RFPA3D is that it can numerically simulate the evolution of cracks in three-dimensional space, as well as the heterogeneity of the rock mass. First, numerically simulated Brazilian tests are compared with experimental results. Special attention is given to the effect of the thickness to radius ratio on the failure modes and the peak stress of specimens. The effects of the compressive strength to tensile strength ratio (C/T), the loading arc angle (2a), and the homogeneity index (m) are also studied in the numerical simulations. Secondly, the failure process of a rock disc with a central hole is studied. The effects of the ratio of the internal hole radius (r) to the radius of the rock disc (R) on the failure mode and the peak stress are investigated. Thirdly, the influence of the vertical and horizontal eccentricity of an internal hole on the initiation and propagation of cracks inside a specimen are simulated. The effect of the radius of the eccentric hole and the homogeneity index (m) are also investigated.

Kavetski D, Binning PJ, Sloan SW, 'Adaptive time stepping and error control in a mass conservative numerical solution of the mixed form of Richards equation', Advances in Water Resources, 24 595-605 (2001) [C1]

This paper presents a new finite element formulation of the upper bound theorem. The formulation uses a six-noded linear strain triangular element. Each node has two unknown veloc... [more]

This paper presents a new finite element formulation of the upper bound theorem. The formulation uses a six-noded linear strain triangular element. Each node has two unknown velocities and each corner of a triangle is associated with a specified number of unknown plastic multiplier rates. The major advantage of using a linear strain element, rather than a constant strain element, is that the velocity field can be modelled more accurately. In addition, the incompressibility condition can be easily satisfied without resorting to special arrangements of elements in the mesh. The formulation permits kinematically admissible velocity discontinuities at specified locations within the finite element mesh. To ensure that finite element formulation of the upper bound theorem leads to a linear programming problem, the yield criterion is expressed as a linear function of the stresses. The linearized yield surface is defined to circumscribe the parent yield surface so that the solution obtained is a rigorous upper bound. During the solution phase, an active set algorithm is used to solve the resulting linear programming problem. Several numerical examples are given to illustrate the capability of the new procedure for computing rigorous upper bounds. The efficiency and accuracy of the quadratic formulation is compared with that of the 3-noded constant strain formulation in detail.

This paper presents a discrete modelling approach which allows the simulation of rockfalls behind drapery systems. The falling rock is represented by a rigid assembly of spheres w... [more]

This paper presents a discrete modelling approach which allows the simulation of rockfalls behind drapery systems. The falling rock is represented by a rigid assembly of spheres whereas the slope is represented by triangular elements. Energy dissipation during impact on the slope is considered via friction and viscous damping. The drapery is represented by a set of spherical particles which interact remotely. The numerical model is used to investigate the efficiency of a drapery system. Various simulations with two different block sizes are performed and the numerical predictions of simulations with drapery are compared to simulations without drapery in order to assess the performance of the protection system.

Research Collaborations

The map is a representation of a researchers co-authorship with collaborators across the globe. The map displays the number of publications against a country, where there is at least one co-author based in that country. Data is sourced from the University of Newcastle research publication management system (NURO) and may not fully represent the authors complete body of work.

Professor Scott Sloan and Dr Chet Vignes have been awarded more than $453,000 in ARC Discovery Project funding commencing in 2015 for their research project Computational modelling of hydraulic fracture.